Middlesbrough's preparations for Saturday's FA Cup third-round tie at Brentford have been affected by positive Covid-19 cases within first-team players and staff.
First-team and under-23 players as well as staff were tested for a second time on Thursday, before the tie.
Derby confirmed a similar outbreak before their FA Cup tie at Chorley.
The Rams have isolated their entire first-team squad and first-team coaches, including interim boss Wayne Rooney, for the game and will instead field a side comprising of under-23 and under-18 players.
Boro boss Neil Warnock could be forced to follow suit, with the under-23 squad within the testing programme as part of the club's preparations for the cup fixture.